LIMA, July 15 (Reuters) - Protesters blocked a portion of Peru's main coastal highway on Monday in the start of a new challenge to a billion-dollar copper mining project that has been a lightning rod for conflict.

Protesters from the area bordering Southern Copper Corp's $1.4 billion Tia Maria copper mine project in the south of Peru carried signs and flags as they occupied a section of the highway, snarling traffic for cargo vehicles and others.

The project has long been lamented by residents in the southern region of Arequipa where farmers say the mine will pollute their fields and affect water supplies.

"We are not going to talk. We want the presence of President (Martin) Vizcarra with the cancellation of the project," Luis Cornejo, mayor of Cocachacra, told Reuters, referencing the construction permit granted by the government on July 9.

Southern Copper spent years awaiting the final green light that former governments had declined to give because of fears it would revive deadly protests that previously derailed the project. At least six protesters were killed in clashes with police in 2011 and 2015. The company said it would not begin construction until it gains more support from people who live in the area.

Southern Copper declined to comment on Monday's demonstrations.

Peruvian Prime Minister Salvador del Solar said on Monday that the government is open to discussions with provincial government officials, but had not yet received a response. (Reporting by Marco Aquino; writing by Cassandra Garrison; editing by Grant McCool)